<form action="https://www.sandbox.paypal.com/cgi-bin/webscr" method="post">
    <input type='hidden' value="Montant_Achat" name="12" />
    <input name="currency_code" type="hidden" value="EUR" />
    <input name="shipping" type="hidden" value="0.00" />
    <input name="tax" type="hidden" value="0.00" />
    <input name="return" type="hidden" value="http://votredomaine/paiementValide.php" />
    <input name="cancel_return" type="hidden" value="http://votredomaine/paiementAnnule.php" />
    <input name="notify_url" type="hidden" value="http://votredomaine/validationPaiement.php" />
    <input name="cmd" type="hidden" value="_xclick" />
    <input name="business" type="hidden" value="fab_1333623840_biz@gmail.com" />
    <input name="item_name" type="hidden" value="Nom de votre produit" />
    <input name="no_note" type="hidden" value="1" />
    <input name="lc" type="hidden" value="FR" />
    <input name="bn" type="hidden" value="PP-BuyNowBF" />
    <input name="custom" type="hidden" value="ID_ACHETEUR" />
    <input alt="Effectuez vos paiements via PayPal : une solution rapide, gratuite et sécurisée" name="submit" src="https://www.paypal.com/fr_FR/FR/i/btn/btn_buynow_LG.gif" type="image" /><img src="https://www.paypal.com/fr_FR/i/scr/pixel.gif" border="0" alt="" width="1" height="1" />
</form>